1. Field of the Invention
The present invention is directed to a method of measuring irregularities in a pneumatic tire.
2. Description of the Related Art
One method of measuring irregularities of a pneumatic tire comprises rolling the tire in an inflated condition in a rotary mounting arrangement and under a predetermined preload against a test surface, and measuring the reaction forces which occur in that operation, in the form of a force fluctuation diagram. Such a method is to be found, for example, in the publication "Werkstatt und Betrieb 103' (1970), pages 183 through 188. More specifically, that method involves investigating the spring behavior or spring characteristics of a tire which rolls under a loading against a test drum, in two mutually perpendicular axes. As an alternative to a test drum, the test surface against which the inflated tire is rolled may be an endless belt which passes around first and second guide or deflection rollers and on which the tire to be tested is supported. The reaction forces which occur during the rolling movement of the tire against the test surfaces are usually detected in the form of tangential, radial and lateral forces. The force fluctuation diagrams which are produced in the measuring procedure by virtue of measurement of the reaction forces occurring provide information about the irregularity of the tire.
The rotary mounting arrangement for supporting the inflated tire in the measuring procedure may be in the form of measuring rim members, between which the pneumatic tire is held in an inflated condition, in the testing machine. It is also possible for the pneumatic tire, when fitted to a disk wheel, to be introduced in an inflated condition into the testing machine. In that case the wheel is mounted in a clamping and centering assembly, rotatably about the axis of rotation thereof.
Radial runout and lateral runout deviations of the measuring rim members of the testing machine, or centering defects in the clamping and centering mounting assembly, give rise to error values which are contained in the resulting force fluctuation diagram with respect to the reaction forces to be measured. The errors falsify the force fluctuation diagram which is intended to provide information about the quality of the pneumatic tire. For example, a radial run-out error in the measuring rim member in the form of a deviation of 0.1 mm, depending on the structure of the respective pneumatic tire to be tested, can give rise to an error, for example, in the radial force of about 10-20N. In addition, when using measuring machines with divided measuring rim members, the rim member halves do not remain properly associated with each other in terms of positioning. Therefore, different radial run-out deviations in the two measuring rim members have different effects on the tire beads and related parts of the tire, depending on the respective position of the two measuring rim members relative to each other.